Study Set Content:
221. A reversed Carnot has a refrigerating COP of 2.5. Determine the ratio TH/TL.
A. 1.4 B. 1.5 C. 1.25 D. 1.2
A. 1.4
222. Three thousand cubic feet per minute of air are circulated over an air-cooled condenser. If
the load on the condenser is 64,800 Btu/hr, compute the temperature rise of the air passing
over the condenser. Specific volume of standard air (13.34 ft3
/lb).
A. 10°F B. 15°F C. 20°F D. 25°F
C. 20°F
223. Saturated vapor ammonia at -16°C (hT = 1442.60 kJ/kg) leaves the evaporator and enters
the compressor at -6°C (h1 = 1465 kJ/kg). The refrigerant leaves the condenser as saturated
liquid at 40°C (h4 = 390.6 kJ/kg) and enters the expansion valve at 35°C (h5 = 366.1 kJ/kg). Heat
rejected from the condenser amount to 50 kW. The work to compressor is 208 kJ/kg, while the
heat loss from compressor is 33 kJ/kg. If 95 kJ/kg of heat are lost in the piping between the
compressor discharge and condenser inlet, determine the refrigerating capacity of the system.
A. 49.5 TR B. 46.61 TR
C. 12.88 TR D. 13.24 TR
D. 13.24 TR
224. In an actual refrigeration cycle using R12 as working fluid, the refrigerant flow rate is 0.05
kg/s. Vapor enters the expansion valve at 1.15 MPa, 40°C (h = 238.5 kJ/kg) and leaves the
evaporator at 175 kPa, -15°C (h = 345 kJ/kg). The electric iput to motor driving the compressor
is measured and found 3.0 kW. Motor efficiency at this load 92% and mechanical efficiency
82%. Determine the actual coefficient of performance for this cycle.
A. 1.58 B. 2.36 C. 1.78 D. 1.3
B. 2.36
225. In an ammonia refrigeration system, the temperature in the evaporator is -12°C and the
ammonia at the evaporator entry 0.1511 dry while at exit is 0.95 dry. If the rate of ammonia
circulation is 5.64 kg/min, determine the refrigerating capacity of the system. Enthalpy of
saturated liquid and vapor at -12°C is 144.929 kJ/kg and 1447.74 kJ/kg respectively.
A. 17.82 B. 34.82 C. 27.82 D. 4.82
. 27.82
226. A two stage cascade vapor compression refrigeration system uses ammonia in the low-
temperature loop and R-12 in the high-temperature loop. The ammonia provides 15 tons of
cooling. If the high-loop temperature requires 10.12 kW compressor power and low loop 15.93
kW, determine the COP of the system.
A. 2.027 TR B. 5.22 TR C. 3.314 TR D. 9.1 TR
A. 2.027
227. When a man returns to his well-sealed house on a summer day, he finds that the house is
at 32°C. He turns on the air conditioner, which cools the entire house to 20°C in 15 min. If COP
of the air conditioner system is 2.5, determine the power drawn by the air conditioners.
Assume the entire mass within the house is equivalent to 800 kg of air for which c = 0.72 kJ/kg -
°C.
A. 7.08 kW B. 3.07 kW C. 19.2 kW D. 12.08 kW
B. 3.07 kW
228. It is desired to double the COP of a reversed Carnot engine for cooling from 5.0 by raising
the temperature of heat addition while keeping the temperature of heat rejection constant. By
what percentage must the temperature of heat addition be raised?
A. 10.1% B. 9.1% C. 8.1% D. 7.1%
B. 9.1%
229. An ammonia water-cooled compressor receives the refrigerant at specific volume 62 L/kg.
It has a piston displacement rate of 5 m3
/min. If a squirrel cage motor running at 1200 rpm
drives the compressor and average piston speed is 490 m/min, calculate size of cylinder bore.
A. 20.4 cm B. 26.0 cm C. 16.13 cm D. 13.6 cm
C. 16.13 cm
230. If the initial volume of an ideal gas is compressed the one-half its original volume and to
twice its temperature, the pressure:
A. Doubles B. Quadruples
C. Remains constant D. Halves
. Quadruples
231. If the gage pressure of a medium is 30 kPa (vacuum) and the atmospheric pressure is 101.3
kPa, the absolute pressure will be?
A. 131.3 kPa B. -71.3 kPa
C. 71.3 kPa D. -131.3 kPa
C. 71.3 kPa
232. If a particle has a velocity of 4 meters per second and a kinetic energy of 144 Joules, then
the mass, in kilograms of this particle must be?
A. 44 B. 16 C. 18 D. 24
C. 18
233. A condenser vacuum gauge reads 715 mm Hg when the barometer stands at 757 mm Hg.
State the absolute pressure in the condenser in kN/m2
or kPa.
A. 5.6 kPa B. 5.9 kPa C. 6.5 kPa D. 5.2 kPa
A. 5.6 kPa
234. Determine the force in newton in a piston of 465 mm2
area with a pressure of 0.172 MPa.
A. 65 N B. 72 N C. 80 N D. 111 N
C. 80 N
235. One piston of a hydraulic press has an area of 1 cm2
. The other piston has an area of 25
cm2
. If a force of 150 N is applied on the smaller piston, what will be the total force on the
larger piston if both piston surfaces are on the same level?
A. 6 N B. 175 N C. 3750 N D. 4250 N
C. 3750
236. The work done on air is 10.86 kJ/kg, determine the compressor power if it is receiving 272
kg/min of air.
A. 36.72 hp B. 49.23 hp C. 2954 hp D. 66 hp
D. 66 hp
237. A water tank 18 ft wide, 14 ft long, and 4 ft high, calculate the pressure at the bottom of
the tank.
A. 1.733 psi B. 1.999 psi
C. 2.337 psi D. 3.773 psi
A. 1.733 psi
238. What is the pressure of 750 mm Hg in kN/m2
?
A. 90 B. 100 C. 103 D. 110
B. 100
239. A double purpose tank 18 ft wide, 24 ft long and 4 ft depth is filled with water. What is the
weight of water in the tank in long tons?
A. 49 tons B. 48 tons C. 54 tons D. 50 tons
A. 49 tons
240. Oil flows through a 16 tube single cooler with a velocity of 2 m/s. The internal diameter of
the tube is 30 mm and oil density is 0.85 gm/ml. Find the volume flow in liters per sec.
A. 22.62 B. 32.22 C. 62.22 D. 42.62
A. 22.62
